Laminated fibrous structures and methods for their manufacturing are well known in the papermaking art. Laminated fibrous structures are created by a variety of ways, including embossing two or more individual fibrous sheets (also called plies or laminae) and adhesively joining them together. The resulting laminates have been employed for a variety of products ranging from packaging and construction materials to household paper products, such as paper tissues, table napkins, place mats, paper towels, and the like.
To perform their intended tasks and to find wide acceptance, the household laminated paper products must exhibit certain physical characteristics. A typical consumer desires the household paper product to have a high quality cloth-like appearance, a relatively thick caliper, and an aesthetically pleasing pattern. All of these physical characteristics must be provided without sacrificing the other desired qualities of strength, softness, and absorbency of the paper product.
Strength is the ability of a paper web to retain its physical integrity during use.
Softness is the pleasing tactile sensation customers perceive when they crumple the paper in their hands and while using the paper for its intended purposes.
Absorbency is the characteristic of the paper which allows it to take up and retain fluids, particularly--water and aqueous solutions and suspensions. In evaluating the absorbency of paper, not only is the absolute quantity of fluid a given amount of paper will hold significant, but the rate at which the paper will absorb the fluid is also important. In addition, when the paper is formed into a product such as a towel or wipe, the ability of the paper to cause a fluid to be taken up into the paper and thereby leave a dry wiped surface is also important.
It is well known in the papermaking art that embossing generally increases absorbency, softness and bulk of the household paper products, such as toilet tissue, paper towel, napkins and the like. There are several common patterns of embossed laminated paper structure intended for the household products: nested (also known as "mated" or "male-female") pattern, knob-to-knob pattern, continuous pattern, and dual ply lamination. All these patterns are associated with the use of a pair of patterned, and axially parallel embossing rolls. During the process, the embossed sheets of paper are fed through a nip formed between two juxtaposed embossing rolls. Discrete protuberances or raised continuous surfaces on the embossing rolls compress regions of each sheet into engagement and contacting relationship with the opposing sheet according to a preselected pattern. The compressed regions of the sheets provide for joining of and maintaining the sheets in a face-to-face contacting relationship.
Specifically, in a knob-to-knob pattern, the discrete protuberances (or "knobs") on one embossing roll are registered with the protuberances on the opposing embossing roll. In a nested pattern, the protuberances of one embossing roll mesh between the protuberances of the other embossing roll. In the continuous pattern, the raised continuous surfaces (as opposed to the discrete protuberances of the knob-to-knob pattern) of one of the embossing rolls are registered with the raised continuous surfaces of the other roll. The knob-to-knob pattern is described in the commonly assigned U.S. Pat. No. 3,414,459 issued to E. R. Wells on Dec. 3, 1968, which patent discloses the compressible paper structures formed by embossing identical raised patterns of discrete protuberances on two extensible paper sheets. The mated distal surfaces of the embossed protuberances are adhesively joined, and the resulting laminated paper structure is calendered. This patent is incorporated by reference herein. The dual ply lamination type is disclosed in the commonly assigned U.S. Pat. Nos. 5,294,475, issued on Mar. 15, 1994 to McNeil and 5,468,323 issued on Nov. 21, 1995 to McNeil, which patents are incorporated by reference herein. The McNeil patents disclose a dual ply laminate having two laminae which are embossed such that each embossed site of one lamina is adhesively joined to the non-embossed region of the other lamina.
The examples of various patterns are illustrated in the prior art by U.S. Pat. No. 3,547,723, issued Dec. 15, 1970 to Gresham; U.S. Pat. No. 3,556,907 issued on Jan. 19, 1971 to Nystrand; U.S. Pat. No. 3,708,366, issued Jan. 2, 1973 to Donnelly; U.S. Pat. No. 3,738,905, issued Jan. 12, 1973 to Thomas; U.S. Pat. No. 3,867,225 issued Feb. 18, 1975 to Nystrand; U.S. Pat No. 4,483,728 issued Nov. 20, 1984 to Bauernfeind; U.S. Pat. No. 4,921,034 issued May 1, 1990 to Burgess; U.S. Pat. No. 5,269,983 issued Dec. 14, 1993 to Schulz; U.S. Pat. No. 5,356,364, issued Oct. 18, 1995 to Veith et al.; U.S. Pat. No. 5,503,896 issued Apr. 2, 1996 to Veith et al.; and U.S. Pat. No. 5,529,563 issued Jun. 25, 1996 to Veith et al. The commonly assigned U.S. Pat. Des. No. 239,137 issued Mar. 9, 1976 to Appleman illustrates an embossing pattern found on commercially successful paper toweling.
Different attempts have been made in the art to improve upon the embossments caused by the embossing process. For example, attempts have been made to provide embossed patterns having different depths, and asymmetric embossments. Other attempts have been made in the art to provide embossments having a certain size and representing a particular surface area of the embossed sheet. Yet other attempts in the art teach a particular angle, relative to the machine direction of manufacture, for the embossments. Still another attempts have been made in the art to provide embossments having particular configuration. Other attempts teach particular sizes of the protuberances and the corresponding recesses on the juxtaposed embossing rolls. Examples of the attempts to improve upon the embossments are illustrated in U.S. Pat. No. 4,320,162, issued Mar. 16, 1982 to Schulz, et al; U.S. Pat. No. 4,659,608, issued Apr. 21, 1988 to Schulz; U.S. Pat. No. 4,921,034 issued May 1, 1990 to Burgess et al; U.S. Pat. No. 3,940,529, issued Feb. 24, 1976 to Hepford, et. al; U.S. Pat. No. 4,325,773, issued Apr. 20, 1982 to Schulz; U.S. Pat. No. 4,487,796, issued Dec. 11, 1984 to Lloyd et. al; and U.S. Pat. No. 3,961,119, issued Jun. 1, 1976 to Thomas.
Regardless of the particular type of embossing and pattern of lamination, paper laminates of the prior art are formed by rigidly binding two or more sheets of paper together to create a laminated structure. The individual sheets of a laminated structure of the prior art are joined in a number of ways, including both adhesive bonding and mechanical bonding. Lamination/embossing is known to be helpful to increase caliper of the laminated structure and compressibility normal to the plane of the laminated structure, and therefore--to increase the softness associated with the increased compressibility of the structure. An increase in caliper also generally improves the absorbency of the laminated product. At the same time, lamination/embossing of the prior art tends to reduce flexibility of the resulting laminated structure--because the adhesive or mechanical joining utilized by the prior art to bind two or more laminae together forms a rigid connection between the two or more laminae. The increase in caliper, while providing a higher compressibility and associated softness, decreases flexibility of the laminated structure of the prior art. In other words, a trade-off exists between the caliper and compressibility/softness of a laminated structure achieved by lamination and the flexibility of the laminated structure.
Therefore, it is an object of the present invention to decouple the caliper and softness of a laminated structure from the flexibility of the laminated structure.
It is another object of the present invention to produce a strong, soft and flexible laminated structure comprising two or more sheets which are movable relative to each other without separation or tearing of either one of these sheets.
It is still another object of the present invention to provide a process for producing such a laminated structure.